Java使用SAX解析xml的示例

<?xml version="1.0" encoding="utf-8"?>
<persons>
  <user>
    <userId>1001</userId>
    <userName>张三</userName>
  </user>
  <user>
    <userId>1002</userId>
    <userName>李四</userName>
  </user>
</persons>

public class Customhandler extends DefaultHandler2 {

  List<Map> list = new ArrayList<>();
  Map map = null;
  String tag = "";

  @Override
  public void startDocument() throws SAXException {
    System.out.println("开始解析xml");
  }

  @Override
  public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
    System.out.println("开始解析元素: <"+ qName + ">");
    if(qName == "user"){
      map = new HashMap();
    }
    tag = qName;
  }

  @Override
  public void characters(char[] ch, int start, int length) throws SAXException {
    String text = new String(ch, start, length).trim();
    if(text != null && !text.isEmpty() && tag!=null&& tag!=""){
      map.put(tag, text);
      if(!map.containsKey(tag)){
      }
      System.out.println("解析到元素值："+ text);
    }
  }

  @Override
  public void endElement(String uri, String localName, String qName) throws SAXException {
    System.out.println("结束解析元素: <"+ qName + ">");
    if(qName.equals("user")){
      list.add(map);
    }
    tag = "";
  }

  @Override
  public void endDocument() throws SAXException {
    System.out.println("结束解析xml");
  }
}

public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException {
  //创建xml解析工厂
  SAXParserFactory factory = SAXParserFactory.newInstance();
  //创建xml解析对象
  SAXParser parser = factory.newSAXParser();
  File file = new File("test/custom/user.xml");
  InputStream inputStream = new FileInputStream(file);
  Customhandler customhandler = new Customhandler();
  //方式一
  //parser.parse(inputStream, customhandler);

	//方式二
  InputSource source = new InputSource(file.toURI().toURL().toString());
  XMLReader xmlParser = parser.getXMLReader();
  xmlParser.setContentHandler(customhandler);
  xmlParser.parse(source);
  List c = customhandler.list;
  inputStream.close();
}


//打印结果为：
开始解析xml
开始解析元素: <persons>
开始解析元素: <user>
开始解析元素: <userId>
解析到元素值：1001
结束解析元素: <userId>
开始解析元素: <userName>
解析到元素值：张三
结束解析元素: <userName>
结束解析元素: <user>
开始解析元素: <user>
开始解析元素: <userId>
解析到元素值：1002
结束解析元素: <userId>
开始解析元素: <userName>
解析到元素值：李四
结束解析元素: <userName>
结束解析元素: <user>
结束解析元素: <persons>
结束解析xml

//org.apache.tomcat.util.digester.Digester#parse(org.xml.sax.InputSource)
public class Digester extends DefaultHandler2 {
  
  //读取解析xml
  public Object parse(InputSource input) throws IOException, SAXException {
    configure();
    getXMLReader().parse(input);
    return root;
  }
  
  //对每个xml标签进行解析，并执行于之对应的Rule规则列表
  public void startElement(String namespaceURI, String localName, String qName, Attributes list)
    throws SAXException {
    boolean debug = log.isDebugEnabled();
    // Parse system properties
    list = updateAttributes(list);
    // Save the body text accumulated for our surrounding element
    bodyTexts.push(bodyText);
    bodyText = new StringBuilder();
    // the actual element name is either in localName or qName, depending
    // on whether the parser is namespace aware
    String name = localName;
    if ((name == null) || (name.length() < 1)) {
      name = qName;
    }

    // Compute the current matching rule
    StringBuilder sb = new StringBuilder(match);
    if (match.length() > 0) {
      sb.append('/');
    }
    sb.append(name); //根据每次xml节点的名称拼接成匹配url
    match = sb.toString();

    // Fire "begin" events for all relevant rules(根据namespaceURI匹配获取的Rule规则列表，有顺序规则)
    List<Rule> rules = getRules().match(namespaceURI, match);
    matches.push(rules);
    if ((rules != null) && (rules.size() > 0)) {
      for (Rule value : rules) {
        try {
          Rule rule = value;
          if (debug) {
            log.debug(" Fire begin() for " + rule);
          }
          //依次执行begin方法
          rule.begin(namespaceURI, name, list);
        } catch (Exception e) {
          log.error("Begin event threw exception", e);
          throw createSAXException(e);
        } catch (Error e) {
          log.error("Begin event threw error", e);
          throw e;
        }
      }
    } else {
      if (debug) {
        log.debug(" No rules found matching '" + match + "'.");
      }
    }

  }
}

<Service name="Catalina">

  <Connector port="8081" protocol="HTTP/1.1"
        connectionTimeout="20000"
        redirectPort="8443" />

  <Engine name="Catalina" defaultHost="localhost">

     <Host name="localhost" appBase="webapps"
        unpackWARs="true" autoDeploy="true">
     </Host>
  </Engine>
</Service>